1. Field of the Invention
The present invention relates to a compact surface-mount type antenna and an antenna apparatus for use in mobile communication equipment such as a cellular phone.
2. Description of the Related Art
Recently, in keeping with rapid advancement of down-sized, lightweight, and high-performance mobile communication equipment such as a cellular phone, miniaturization and high performance have come to be increasingly demanded of an antenna which constitutes such equipment. To meet such demands, for example, a surface-mount type antenna has hitherto been developed.
Now, a surface-mount type antenna of conventional design and an antenna apparatus incorporating the antenna will be described with reference to a perspective view shown in FIG. 7.
In FIG. 7, reference numeral 90 represents a surface-mount type antenna. The surface-mount type antenna 90 is mounted on a mounting substrate 96, thus constituting an antenna apparatus 101. In the surface-mount type antenna 90 shown in FIG. 7, reference numeral 91 represents a substantially rectangular parallelepiped base body; 92 represents a feeding terminal; 93 represents a ground terminal; and 94 represents a radiating electrode. Moreover, in the mounting substrate 96, reference numeral 97 represents a substrate; 98 represents a feeding electrode; 99 represents a ground electrode; and 100 represents a ground conductor layer.
In the conventional surface-mount type antenna 90, the feeding terminal 92 and the ground terminal 93 are formed on the side surface of the base body 91. The radiating electrodes 94, which is routed as a long conductor pattern, is formed so that their ends extend upwardly from the ground terminal 93 on the side surface, is then substantially U-shaped as viewed plane-wise, on the top surface of the base body 91 to form nearly a loop, and extend downwardly from the side surface downwardly toward the feeding terminal 92. The capacity of the radiating electrode 94 is controlled by providing a part of a vicinity of the feeding terminal 92 of the radiating electrode 94 with a gap 95, in order to match the impedance with the feeding electrode 98 (feeding line) of the mounting substrate 96.
Meanwhile, in the mounting substrate 96, on the top surface of the substrate 97 are arranged the feeding electrode 98, the ground electrode 99, and the ground conductor layer 100. The ground conductor layer 100 is arranged face to face with one side of the ground electrode 99 and has connection with the ground electrode 99.
Then, the surface-mount type antenna 90 is mounted on the top surface of the mounting substrate 96, with the feeding terminal 92 connected to the feeding electrode 98, and the ground terminal 93 connected to the ground electrode 99. Thereupon, the antenna apparatus 101 is realized.
The related art is disclosed in Japanese Unexamined Patent Publication JP-A 9-162633 (1997).
However, the conventional surface-mount type antenna. 90 poses the following problems. By adjusting the size of the gap 95 which is formed in the radiating electrode 94 to achieve impedance matching between the radiating electrode 94 and the feeding electrode 98, the impedance of the radiating electrode 94 can be changed. Simultaneously, however, the resonant frequency of the antenna varies with the change of the impedance. This makes it difficult to attain the desired antenna characteristics as designed.